Cardiovascular disease, including atherosclerosis, is a leading cause of death in the U.S. A number of methods and devices for treating coronary heart disease have been developed, including a broad array of catheters and minimally invasive methods for using them. Catheter-based delivery systems are routinely used to introduce stents and other medical devices into the cardiovascular system for both therapeutic and diagnostic purposes.
Typically, the catheter is inserted into the vascular system percutaneously through an artery, such as the femoral, jugular, or radial artery. The catheter is threaded through the vascular system until the distal end of the catheter is adjacent to the treatment site. The position of the catheter end may be determined by common visualization methods such as fluoroscopy or ultrasound.
In order to perform well, a catheter must have sufficient columnar strength and rigidity so that it can be pushed through the vasculature of the patient without bending back on itself or kinking. However, if it is too stiff; it may cause damage to blood vessel walls. At the same time, the catheter must be sufficiently flexible so that it can follow a winding, sometimes tortuous, path through the patient's vasculature. In order to balance the need for both flexibility and columnar strength, catheters are frequently constructed to have a relatively rigid proximal section and a more flexible distal section. Such a balanced combination also provides a catheter with good steerability, which is the ability to transmit substantially all rotational inputs from the proximal end to the distal end.
Available catheters attempt to achieve this balanced combination by using support layers of braided and/or coiled filaments within the wall of the catheter. A coiled support layer reinforces the catheter body against crushing, kinking or radial expansion from internal pressure, while adding negligible bending stiffness to the composite catheter structure. A braided support layer also provides resistance to crushing, kinking or radial expansion from internal pressure, while adding substantial torsional stiffness, and may add bending stiffness to the catheter.
The braided and/or coiled material is positioned along at least a portion of the length of the catheter. Where prior art catheters incorporate both braided and coiled support layers, the catheters are manufactured such that the braided material either overlaps or abuts the coiled material as the braided material transitions to the coiled material. One drawback to the overlapping and abutting transitions between the braid and coil is that the manufacturing process requires additional steps for joining the ends of the two types of layers. Another drawback is that such discontinuities between the different types of materials may create undesirable additional thickness and/or stiffness, or a weakness at the point of joining that affects the flexibility, steerability and kink-resistance of the catheter.
The additional torsional and bending stiffness of a braided layer is often a drawback for devices that must be flexible enough to travel tortuous vessels. Prior devices have attempted to limit or decrease the stiffness in areas along the length of the catheter by changing the pick count per inch (PPI) or changing the braid angle. However, changing PPI is done by altering the relative rates of linear motion and rotary motion on a braiding machine while the same number of filaments remains in the weave. As such, these changes are gradual changes that do not allow an abrupt change in stiffness along the catheter.
It would be desirable, therefore, to provide a catheter that overcomes these and other disadvantages.